1. Field of the Invention
The present invention relates to a calibration device for improving the precision of a clock signal, particularly for electronic circuits connected to an interconnect network to which they send a send signal and by which they receive a receive signal, and, more particularly microcontrollers that are clocked by a clock signal.
2. Description of the Related Art
A microcontroller is an integrated circuit that comprises an oscillator for producing the clock signal, a processor, a program memory, a data memory, and peripherals, including in particular a generator for generating interrupts of the processor.
A quartz oscillator is widely used as a result of the very high precision of the frequency of the clock signal it produces. However, this oscillator is costly and has relatively high power consumption, such that it is not suitable for certain applications, particularly in the automotive field.
For these applications, a cheaper component that consumes less power is therefore preferred, such as an oscillator that uses a resonant circuit formed by a resistor and a capacitor, the tuning frequency of this resonant circuit determining the frequency of the clock signal. This type of oscillator, which is well known by those skilled in the art, is traditionally called an RC oscillator, with reference to the initials of the components of the resonant circuit. Ring oscillators, among others, which can also be suitable for these applications, are also known.
The frequency of the clock signal delivered by these oscillators is considerably imprecise mainly due to the dispersion of the characteristics during the manufacturing, although this frequency does not drift substantially in time. While this imprecision can be tolerated by the processor, this is not the case for certain applications.
Most of the control applications in motorcars, such as windscreen wiper control or door module control, are synchronized over a time base. This time base is delivered by a counting module (“TIMER”) dividing the local clock signal. This counting module periodically generates interrupts. Upon each interrupt, a state machine evaluates the value of its inputs and calculates the following state of its outputs. The advantage of this state machine is its determinism which, to be able to be guaranteed, requires a precise time base.